The present invention relates to cleaning solutions and, more particularly, to low-foaming cleaning solutions for removing organic soils from hard surfaces.
Low-foaming cleaning solutions useful in removing organic soils, including protein and glyceride-based deposits, are commonly used to clean equipment or utensils in the food processing, dairy, health care, dental and veterinary industries. Equipment used in the food and dairy industries are often cleaned xe2x80x9cin-placexe2x80x9d by circulating a cleaning solution repeatedly through liquid-carrying pipes of the equipment. In the cleaning of medical, veterinary and dental utensils, items are enclosed in a washing chamber of a washing machine and sprayed with a wash solution which is collected from the washing chamber and recirculated to be sprayed again onto the utensils. This cycle repeats continuously for a predetermined period of time or number of cycles. Foam buildup is objectionable in the above circumstances as it will increase the amount of entrapped air in the recirculating solution. This results in cavitation at the pump or in the recirculating pump losing its prime.
Known low-foaming cleaning solutions include chlorine-based cleaners of high alkalinity, or formulations containing one or more enzymes in a basic solution. Chlorine-based cleaners and enzyme-based cleaners work by breaking large protein, linked amino-acid, glyceride or fatty acid molecules through oxidation and enzymatic action, respectively. The chlorine-based cleaners are based on the high oxidative power of chlorine in combination with an alkaline medium to reduce these large soil particles to smaller units easily dissolved or emulsified by the surface active species present. Similarly, enzymatic cleaners rely on high alkalinity and the chemical breakdown of peptide bonds in proteins for dissolution of soils. In both cases, alkaline conditions result in saponification of fats in the soil, further contributing to the detergency process. Though the actual mechanisms for removing soils differ in both types of cleaning solutions, the effects are similar, namely, large particles are broken down into smaller more water soluble units that are eventually dissolved in the wash liquor.
Drawbacks of chlorine-based cleaners are that their use produces large amounts of waste water containing high amounts of free chlorine. Furthermore, these cleaners are hazardous if mixed with acid solutions (commonly used in two-step cleaning/sanitizing procedures in certain applications) to produce highly poisonous chlorine gas. Also, these cleaners tend to have very pungent odors, may cause skin and eye irritations, and may permanently damage the substrates to which they are applied.
Enzyme-based cleaners, although quite effective in combating protein and lipid-based soils, generally require high temperatures for effective cleaning. Furthermore, the cost of enzyme-based compositions is considerably higher than the cost of most cleaning chemicals. As a consequence, the cost of cleaning with enzymatic-based compositions is generally prohibitive for large-scale applications, and is largely reserved for specialty applications in health, veterinary and dental care.
Hydrogen peroxide based cleaners have become favored more recently because they are odorless, non-corrosive at concentration levels typically employed for cleaning, safe to material substrates, their breakdown products (oxygen and water) are innocuous, and they can be made at low costs. However, the current art does not contemplate a low-foaming, cleaning solution containing hydrogen peroxide which would be useful in the applications discussed herein.
Until now, it has been necessary to add high detergency surfactants to boost the cleaning power of hydrogen peroxide based solutions, in order to achieve the same levels of cleaning efficiency as that of conventional hypochlorite and enzymatic cleaners. Surfactants (or surface active agents) work to decrease the interfacial tension in a solution to facilitate detachment and emulsification of soils. Unfortunately, surfactants which exhibit good detergency will also result in highly foaming solutions, whereas the use of non- or low-foaming surfactants generally leads to poor cleaning compositions. A common solution to this problem is to add silicone-based foam reducing agents to the wash solution. However, these materials tend to allocate and build up in difficult to reach places in the equipment and instruments which facilitates proliferation of microorganisms.
There is therefore a need for a low-foaming cleaning solution which is effective against organic-based soils, exhibits favorable environmental profiles, and possesses a minimal or no risk to the user or to the substrates being cleaned. The present invention is intended to, at least in part, meet these needs.
U.S. Pat. No. 3,969,258 to Carandang et al discloses an acidic, low-foaming sanitizing solution designed for use in recirculating systems in the food and milk industries. The solution is based on highly foaming anionic surfactants known for their antimicrobial properties, and foam suppressing agents consisting of a C8-C18 aliphatic alcohol, or a C9-C12 alkyl phenol, in combination with a polyvalent metal compound. The cleaning efficiency of the solution is not discussed and the use of hydrogen peroxide as a cleaning agent is not taught or suggested.
U.S. Pat. No. 4,878,951 to Pochard et al teaches alkaline cleaning formulations which are low foaming and therefore suitable for the cleaning in-place of equipment which circulates food or dairy products. The formulations contain a source of chlorine (e.g. hypochlorite) and a mixture of surfactants, one of which is a high-foaming C4-C8 alkylated diphenyl oxide sulfonate and the other of which is a nonionic surfactant which is stable in the formulation within certain concentration ranges and which acts to suppress foaming. The nonionic surfactant is selected from the group of polyoxyethylene/polyoxypropylene block copolymers and polyalkoxylated linear or branched aliphatic alcohols. The reported solutions are highly alkaline with caustic soda used at the rate of 10% w/w of the total solution composition. This reference does not disclose or suggest the use of alternate non-chlorine based oxidizers, such as hydrogen peroxide.
U.S. Pat. No. 5,855,217 to John describes a device, process and formulation for cleaning heavily soiled surfaces in the food industry. The device mixes a caustic detergent solution and an aqueous solution of hydrogen peroxide to form an unstable,.high foaming cleaning formulation which is ejected, under pressure, towards the surface to be cleaned before the hydrogen peroxide breaks down. The process is based on the generation of a cleaning foam containing hydrogen peroxide in an amount from 0.1% w/w to 1.0% w/w. The formulation taught clearly does not have application to recirculating systems where the presence of foam cannot be tolerated.
WO 93/14183 to the Procter and Gamble Company discloses a detergent composition which is stable and remains colorless over time. This is achieved by adding hydrogen peroxide and a metal sequestering agent to high detergency, high foaming anionic and/or nonionic surfactants. These surfactants do not include low-foaming small chain-alkane sulfonates and alkylarenesulfonates.
Numerous hydrogen-peroxide based cleaning compositions have been proposed, none of which appear suitable for applications involving substrates highly soiled with protein, carbohydrate and lipids, where both high detergency and low or no foaming are required. For example, U.S. Pat. No. 5,602,090 to Melikyan et al describes a hard surface cleaning solution comprising hydrogen peroxide, D-limonene, two anionic surfactants, a non-ionic surfactant, and deionized water. Although the low-foaming sodium 1-octane sulfonate (sold under the commercial name Bioterge PAS-8S) is listed as a possible one of the anionic surfactants, the other surfactant components are high-foaming.
U.S. Pat. No. 5,891,392 to Monticello et al teaches an acidic hard surface cleaning and disinfecting composition based on hydrogen peroxide as an active disinfecting constituent, a monohydric alcohol, a glycol ether or butoxypropanol or propoxypropanol, a nonionic surfactant, and an organic acid. All the non-ionic surfactants listed in this reference are high foaming.
U.S. Pat. No. 6,110,883 to Petri et al discloses a hydrogen peroxide-based composition suitable for use as a hard surface cleaner or in laundry applications. The composition further comprises a surfactant selected from a group of high detergency/foaming anionic, nonionic or amphoteric surfactants.
Formulations according to the present invention incorporate hydrogen peroxide and specific anionic surfactants which exhibit low-foaming properties. The formulations are designed for cleaning jobs where foam build up is objectionable and where the control of microbial populations is important. The invention provides both a liquid solution and a dry particulate formulation which may be diluted with water, deionized water, or a mixture thereof, to form the liquid solution. The solution may be in concentrated form for dilution by the end user or in ready-to-use diluted form.
Accordingly, in accordance with a first aspect, the invention provides a low-foaming cleaning solution having a pH of from about 8 to about 11.5, optionally, less than about 11, or less than about 9.5, and also optionally greater than about 9, and consisting essentially of:
a) at least one surfactant selected from the group consisting of C3-C8 alkane sulfonates, C3-C8 alkyl sulfates, C1-C7 alkyl naphthalene sulfonates, polyoxyethylene/polyoxypropylene block copolymers having a polyoxypropylene molecular weight of from about 1500 to about 8500, of which less than about 30% of the total molecular weight is due to the polyoxyethylene portion, and mixtures thereof, in a concentration of from about 0.005% to about 40% w/w of the total solution;
b) at least one active oxygen releasing compound selected from the group consisting of hydrogen peroxide, at least one source of hydrogen peroxide, and mixtures thereof, in an amount effective to produce a hydrogen peroxide concentration of from about 0.005% to about 50% w/w of the total solution;
c) at least one builder in a concentration of from about 0.001% to about 50% w/w, optionally greater than about 0.01% w/w of the total solution; and
d) at least one diluent selected from the group consisting of water, deionized water, and mixtures thereof, to 100% w/w.
The source of hydrogen peroxide may be selected from the group consisting of percarbonate (e.g. sodium percarbonate), persilicate, persulphate, perborate (e.g. sodium perborate monohydrate and sodium perborate tetrahydrate), peroxyacids, dialkyl peroxides, diacyl peroxides, preformed percarboxylic acids, organic peroxides, inorganic peroxides, hydroperoxides, and mixtures thereof.
In one embodiment of the cleaning solution, the at least one surfactant is present in a concentration of from about 0.005% to about 4% w/w and may be less than about 3% w/w, the at least one active oxygen releasing compound is present in an amount effective to produce a hydrogen peroxide concentration of from about 0.005% to about 3% w/w, and the at least one builder is present in a concentration of from about 0.001% to about 11% w/w, all based on the total weight of the solution.
In another embodiment of the cleaning solution, the solution contains hydrogen peroxide in a concentration of from about 1% to about 20% w/w, the at least one builder is at least one cation sequestering agent present in a concentration of from about 0.5% to about 20% w/w, and the at least one surfactant is present in a concentration of from about 0.005% to about 3% w/w, all based on the total weight of the solution.
In yet another embodiment, the at least one surfactant is present in a concentration of from about 1.5% to about 4% w/w, the at least one active oxygen releasing compound is present in an amount effective to produce a hydrogen peroxide concentration of from about 2% to about 3% w/w, and the at least one builder is present in a concentration of from about 6% to about 11% w/w, all based on the total weight of the solution.
In a still further embodiment, the cleaning solution contains hydrogen peroxide in a concentration of from about 2% to about 7% w/w, the at least one builder is at least one cation sequestering agent present in a concentration of from about 0.5% to about 7% w/w, and the at least one surfactant is present in a concentration of from about 0.01% to about 2% w/w, all based on the total weight of the solution.
In another embodiment of the cleaning solution, the at least one surfactant is present in a concentration of from about 0.005% to about 0.03% w/w, the at least one active oxygen releasing compound is present in an amount effective to produce a hydrogen peroxide concentration of from about 0.005% to about 0.03% w/w, and the at least one builder is present in a concentration of from about 0.001% to about 0.10% w/w, all based on the total weight of the solution.
In a still further embodiment, the cleaning solution contains hydrogen peroxide in a concentration of from about 0.005% to about 2% w/w, preferably from about 0.01% to about 1% w/w, the at least one builder is at least one cation sequestering agent present in a concentration of from about 0.01% to about 2% w/w, preferably from about 0.01% to about 1% w/w, and the at least one surfactant is present in a concentration of from about 0.005% to about 3% w/w, preferably from about 0.01% to about 2% w/w, all based on the total weight of the solution.
The at least one surfactant may be selected from the group consisting of alkali metal and ammonium salts of octane sulfonic acid (e.g. sodium octyl sulfonate), alkali metal and ammonium salts of cumene, toluene, xylene sulfonic acids (e.g. sodium xylene sulfonate), a block copolymer consisting of a polyoxyethylene block capped at both ends by polyoxypropylene blocks where the total molecular weight of the polyoxypropylene portion is 1700 and the polyoxyethylene portion comprises about 20% of the total molecular weight, and mixtures thereof.
The at least one builder may be at least one cation sequestering agent selected from the group consisting of citric acid, glycolic acid, polyphosphates obtained by the thermal treatment of monosodium phosphate (e.g. tetrasodium pyrophosphate, sodium tripolyphosphate, sodium tetraphosphate, sodium hexametaphosphate, and mixtures thereof), amino phosphonic acid compounds with 1 to 5 phosphonic acid moieties (e.g. amino tri(methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, diethylenetriaminepenta (methylene phosphonic acid), ethylene diamine tetra(methylene phosphonic acid), and mixtures thereof), amino-carboxylic acid analogues of amino phosphonic acid compounds with 1 to 5 phosphonic acid moieties (e.g. ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, and mixtures thereof), and mixtures thereof.
The cleaning solution may contain at least one corrosion inhibitor for inhibiting corrosion of metallic substrates upon drying, in a concentration of from about 0.005% to about 5% w/w, preferably greater than about 0.01% w/w, and may be up to about 1.5% w/w, of the total solution. The at least one corrosion inhibitor may be selected from the group consisting of C2-C5 polyhydric alcohols (e.g. propylene glycol), triazoles, nitrites (e.g. sodium nitrite), molybdates (e.g. sodium molybdate), benzoates (e.g. 1,2,3-benzotriazole), gluconates, and mixtures thereof.
In accordance with a second aspect, the invention provides a dry particulate cleaning formulation which can be dissolved in water, deionized water, or a mixture thereof, to produce a cleaning solution according to the first aspect of the invention. The dry formulation contains at least one source of hydrogen peroxide which may be selected from the group consisting of sodium percarbonate, sodium perborate monohydrate, and sodium perborate tetrahydrate, and mixtures thereof, at least one builder, which may be a cationic sequestering agent, and at least one surfactant, which may be an anionic surfactant.
The concentration of each component required to provide a solution according to the first aspect of the invention will be readily apparent to the person skilled in the art. For example, in one embodiment, the at least one surfactant is present in an amount of from about 2% to about 20% w/w, the at least one source of hydrogen peroxide is present in an amount of from about 5% w/w to about 30% w/w, and the at least one builder is present in an amount of from about 5% to about 50% w/w, all based on the total weight of the formulation.
In another embodiment of the formulation, the at least one surfactant is present in an amount of from about 2% to about 10% w/w, the at least one source of hydrogen peroxide is present in an amount of from about 15% w/w to about 25% w/w, and the at least one builder is present in an amount of from about 10% to about 20% w/w, all based on the total weight of the formulation.
In other embodiments of the formulation, at least one source of hydrogen peroxide is present in an amount effective to produce a hydrogen peroxide concentration of from about 5% w/w to about 30% w/w, or about 15% w/w to about 25% w/w, when the formulation is dissolved to form an aqueous solution.
The formulation may contain, for every one part by weight of the at least one source of hydrogen peroxide, from about 0.25 to about 4 parts by weight of the at least one builder.
Optionally, the formulation may contain a diluent in the form of at least one inert filler selected from the group consisting of sulfate salts, phosphate salts, silicate salts, carbonate salts, and mixtures thereof.
Liquid cleaning solutions and particulate cleaning formulations according to the invention may be contain at least one buffer in an amount effective to achieve the desired alkaline pH.
In accordance with a third aspect, the invention provides a method of cleaning equipment used to circulate food products, in place, comprising:
(1) providing a cleaning solution according to the first aspect of the invention; and
(2) circulating the liquid cleaning formulation through the equipment to be cleaned at a temperature of 20xc2x0 C. or higher, and preferably at 40xc2x0 C. or higher.
When the term xe2x80x9ccomprisingxe2x80x9d is used herein, it shall be construed to mean xe2x80x9cincluding but not limited to.xe2x80x9d The term xe2x80x9cconsisting essentially ofxe2x80x9d shall be construed to mean xe2x80x9cincluding the listed components or ingredients and such additional components and ingredients which do not materially alter the basic and novel characteristics of the present cleaning solution and particulate formulationxe2x80x9d. For the sake of clarity, the basic and novel characteristics of the present solution and particulate formulation are the cleaning, stability and low-foaming characteristics for a given concentration of components or ingredients. For the sake of clarity, the term xe2x80x9cconsisting essentially ofxe2x80x9d shall be construed to include the listed components or ingredients, plus optional buffers (e.g. caustic salts such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide) to provide a cleaning solution having a pH value in the specified ranges, inert fillers and diluents (e.g. sulfate salts, phosphate salts, silicate salts, carbonate salts, and mixtures thereof), corrosion inhibitors to prevent corrosion of certain metal substrates, and small or trace amounts of other ingredients commonly or typically present in commercially available components or ingredients of the present inventive solution and particulate formulation.
The term xe2x80x9cbuilderxe2x80x9d is used herein to refer to those ingredients in a cleaning solution that, through complexation, (i) eliminate alkaline-earth ions from water, substrate or soils, and (ii) support detergent cleaning action by modifying the electrostatic properties of soils, substrates and wash liquor to enhance the detergency process, prevent soil redeposition, facilitate surfactant action, and influence solution foaming properties. Examples include sequestering agents such as sodium diphosphate, sodium triphosphate, 1-hydroxyethane-1,1-diphosphonic acid, diethylenetriaminepenta (methylene phosphonic acid), nitrilotrimethylene phosphonic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, citric acid and glycolic acid.
Without being limited by any theory herein, it is believed that several mechanisms are responsible for the cleaning performance of the solution. First, hydrogen peroxide oxidizes protein, carbohydrate and lipid molecules and destroys sulfhydryl and double bonds to break the molecules down into smaller units.
Second, builders, including cation sequestering agents (i.e. chelating agents), are believed to play an important role in the emulsification and break-up of soil particles. The builders are relied upon for enhancing detergency by (i) increasing the negative zeta potentials between soil aggregates and substrates, thereby creating an electrostatic repulsive force, and (ii) breaking down soil aggregates which are linked together by mutual cation bridges. Furthermore, chelating agents sequester dissolved cations, thereby minimizing the decomposition rate of the hydrogen peroxide in solution.
Third, the alkaline conditions are believed to have the following effects. The rate of reaction of the hydrogen peroxide with organic soils is enhanced at the pH levels of the invention. These conditions contribute to the development of a greater zeta-potential difference between substrate and soil and amongst soil particles, thereby facilitating detachment of the soil from the substrate and its emulsification in solution. Fatty acids present in many of these soils undergo saponification, thus greatly enhancing their solubility and further providing additional detergent action to, or increasing the surface activity of, the solution as a whole. Reducing the interfacial tension of the solution through surfactants results in better wetting of the soil-substrate and soil-soil interstices, thereby facilitating detachment and break-up.
Furthermore, the surfactants employed should have a high hydrotroping capacity, should produce a reduction of the interfacial tension of the wash liquor, and should not produce substantial amounts of foam. Also, they should have cloud point temperatures above the temperature at which the solutions are used. The expression xe2x80x9ccloud point temperaturexe2x80x9d means the temperature at which a surfactant begins to become insoluble in water and a cloudy dispersion results. The invention will be better understood with reference to the following examples: